Means for recording sound



Jan. 14, 1930. SYKES 1,743,251

MEANS FOR RECORDING SOUND Original Filed Nov. 16. 1920 INVENTOFL:

A. F. snags,

y his Attorneys,

- 30 meet reamed 1e1 1930 'PATENT orrlca ADRIAN FRANCIS SYKES, OF NEW BA BNET,

means non RECORDING sounn Original application filed November 16, 1920, Serial No. 424,421, and in Greatliritaln flove'mher 18, 1819.

Divided and this application. filed May 15, 1925. Serial No. 30,605.

This

lapplication is a division '01 my u. s. Patent 0. 1,711,551, May 7, 1921.

. This invention relatesto apparatus for the conversion of sound into equivalent varia- 'tion of electric currents or potentials and to the conversion of electric currents or derivatives thereof into mechanical vibration for the purpose of reproduction. My two prior Patents No, 1,711,551 and No. 1,639,713, describe means for effecting the first of these objects;

the present specification concerns means for reproduction. I y i v I The principles involved are ver similar in both cases. I presume in the rst place 5 that. true voice currents are required to be represented by mass, a term which is sufiiciently explained in the above specifications. It consists in the present case of an acoustically inert coil carrying a sapphire. The sapphire engages with a wax surface of sufficient softness not materially to interfere with the vibrations which would be induced in the massin the absence of the wax. By wax is meant the usual composition employed in the production:

of master records.

The coil is simply floated on the wax surface for vertical or phonograph recording and suitable m difications are introduced to the needs pf the lateral or gramophone cut. Such a coil when supplied with "currents properly representing the voice, musical performance ,or telephone message, it is desired to record, does not vibrate in a manner truly corresponding .to the electrical variations but on the contrary the waveform of the vibration of the coil differs from that of the electrical current passing through it in a very definite manner; neglectlng the re sistance of the wax to penetration the harmonics are roduced in value in the proportion of 1/ where f is the frequency), that is, they are represented ina manner inversely roportional to the square of the frequency. ence in .my invention the electric currents are in effect distorted artificially before they are suppliedto the ,coil. The correct modifi cation is that the harmonics are magnified in the proportion of the square of the fre uency, which change can be broughtabout y the the displacement of a plainviscosity-a resistance depending upon the only modifies in scale the true voice current use of inductances in the following fashion Supposing the electrical variations available can supply no appreciable power they are in the first place magnified by a thermionic valve relay 'or the like, the last valve of which is fairly powerful. A small inductance is placed in' the plate circuit of this latter valve and the variation of electrical potential on this inductance is the differential of the current in the plate circuit, so that every harmonic is exaggerated in proportion to its frequency. For this to be realized inpract'ice the resistance of the late circuit must be large compared with the impedance of the inductance used for the frequency considered. The potential across the inductance is now caused to operate a second valve also with a small inductance in its plate circuit; thevariation of otential on this second inductance is the di erential of the plate current and hence every harmonlc 1s exaggerated in the proportion of its frequency, so that the variations of potential on this second inductance referred to the original supply of current produced by the voice are exaggerated in the proportion of the square of the frequency.

-Again these variations are caused to operate a third valve designed to supply current to the recording coil, The term coil is to be understood in a broad sense; it may not involve a complete turn if a current transformer is used. A Fessenden vibrator might conceivably be adapted to the case.

Among resistances that may be encountered in apparatus for recording on wax may be mentioned, firstly a thrust from the wax varying with and for small displacements proportional to the departure from the mean position; secondly a resistance of the nature of.

velocity of the moving parts; thirdly the inertia of the recording element itself. Of these resistances which comply with the conditions requisite for a damped tone, the first itself, the second can be corrected by anappropriate fraction of the differential of the voice current, the third by the second differential of the voice current. In the practice of the invention, however, the inertia of the .go The I cases the mass of the detecting or inscribln soun aving instrument corresponds to. 250 virations a second, and should that be the only orated in the system.

'- a ust asin the case of, the detector the rescording coil behaves as a plain mass and not as a resonator as is the diaphragm of a telephone or the like. vA. vibratin" element of telephony or sound recording fortwo' reasons. In the-firstplace it is insensitive, and secondly it distorts thesound. -By the use of relays of" distortionless character ,now available the objection as to sensitiveness disappears; and by suitably modi in'gLthe wave form of the currents before a lowing them v to vibrate the coilthe distortion is'elim n'ated. point of view adopted is that in all agenc is compensated for completely regar less 0 the frequency; while elastic control or viscous damping are either, and preferablyi as made relatively negligible or are provide for b a ropriate currents derived from the hue if the natural period of the enperiod which can be readily excited by the quency' of 1000 vibrat ons a second the mass is largely the predominant factor and so determines the extent of the vibration and the electrical forces are artificially distorted to 7 ensure that the mass will vibrate over the j proper range notwithstanding ,that'th'e' fre' 'quency is much above the natural freguen'cy ealmg.

of the instrument. Theaprinciplefor with any tone which occurs in the a paratus consists in reducingthe electrical orces at the resonance point -to' the amount required to overcome the damping only.

Suppose a detector which erives current the excess pressure wave be available; Alternatively let a detector ex v placement wave be availab e .and subject its potential to a process of differentiation so as to derive a result equivalent to the excess pressure wave. Let this detector control-an amplifying valve in whose plate circuit is placed a large inductance in parallel with a combination of a small inductance, a 'condenser and a resistance all in series and so proplortioned as tobe the electrical equivalent of t e mechanical vibrating system. By'this I mean that the time period is the same and the damping of the same degree. The imgedance of the electrical system must .be suf ciently small as to permit the chain es in valvecurrent to be driven through without sensible modification; With thisstate of af-fi fairs the potential across the combination is 66 such as to compensate for the mass, elasticity other resistances. Neverthe-.

this character is never 'used in practical i system at any instant electrical forces brought to hear, at a, freor potential from the sound equivalent toressing the dis-.

' and damping oft the mechanical system for any frequency up to that; when the impedance .of the electrical'combination becomes com parablewith the resistance of; the valve itself. In relationto theexce'ss pressure'wave of the soundthe potential across I thev condenser fthe-resistance' and the inductance re spectivel'y, is the fluivalent of the unaltered wave, the first I,

The velocity ttaiued by the mechanical is the mechani equivalentyof the plate circuit current; a hence the amplitude developed is the-integra j" ofthat currentawith respectto timed-and therefore corresponds to the displaceni curve of the sound. At the resonant frequent cy the voltageacross the condenser-is e u'al Y and opposite to the voltage acrossthe in tance and therefore the. only potential sh plied to the grid of the next-valveis the po'- tentialac'ros'sthe resistance'which is adjusted v to compensate for the v dam ing o'f'the me-'.-} chanical system. .Additio'na dampingcould fl be provided bym'e'ans eta 4 less shortcircu'ited. a

he reason for paying attention to vthe case I "stability considerable elastic control must be provided otherwisethe armature simply flies tothepoleor'poles. By taking into account this control such a-devicecould be operated on the linesof'my-invention. An example is vfurnished, theldrawin'gs' which were filed, with'the present specification.-- Possibly byloa careful-experimental study of a reed or dia-Tf phragm .teleph I mfintp uldbe improved as a'recorder by com one receiver such 'an instlrii-y pensating foreac I the resonant action more.-uniform.,;. t The recording element most favoured at thepresenttime sa small com act/coil weighing" about}. grammes adapted orttorsional vib'ra-T tionlocated in a sing e magnetic air" duction density about 15,000 c. that is, without iron armature.

weak elastic control purely for facili-f tating the use of a gravity method of-jdeter mining the depth of cut in the wax. H In lace of the ordinary tale hone currents providing. a link bstween the etector" and it is obvious that the detector may control directly or ind rectly a high fre uency transmitting set similar to anyuse ,for wireless of itstones so as'to render.

The coi is telephony and so modulate-acarrier wave but ere'ntial .and the second I differential respectively: a H

v I sup lementaryiso' C011 attachedv tothemain coil 5d more g. s.. mes

the recordcv or musical selections transmitted by wireless vtelephonyfrom distant countries or from modulated carrier currents transmitted by means of wires. Apart from the subiectmatter of this invention, however, all such apparatus and schemes are dealt with in books on,

wireless telegraphy.

-I now turn to the use in combinatio'niof thed'etector andthe recorder. The standard ofreference adopted has been the .wave of excess pressure. Particle displacement v as well as pressure difierence over a'small interval can be derived from. the wave-of excess The detector 713 takes the excess pressure as the standard.

'Ithas been observed that if the process is stopped at the stage when the mass is exposed on one side only 'to the wave of excess pressure and simply netic field, thenthe E. M. F. induced is in terms of particle displacement. British specification No, 160,223 shows such an apparatus coupled to a, recorder suitable for en vaving cordings intermediate between that'of full excess 'ressure and particle displacement can i be obtained b v the use of an inductance 1n one or other of t e, distortion circuits, which in ductance tends more and more merely to check the current-as the frequency rises and I not to differentiate. These remarks are made because in making a record it may be neces- 'saryto take some account of the natural characteristics ofthemachine on which it is intended to reproduce it. My invention enables 1 the operator to compensate to various influenc'es which-would otherwise impair the fidelity of the reproduced sound.

Of'course' if the characteristic of the de- I tecting or reproducing agency supplies one or more of the steps required by my systemas described," then such step or steps would be omitted.

tentials available but some modification thereof, the invention is varied accordingly; in

" fact in the making of a soundrecord theefiect obtained necessarily involves the combination of the detectin instruments.

engraving and reproducing n particular should the phonograph or gramophorie tend togive undue prominence to a harmomc of a particular .pitch, such a harmonic could be taken account of in the recording by shuntin one of the valve transformers with anoscil ation circuit which-at the particular frequency reduces the raph, the recording which in combina- 'duction of the ori nal sound may not itcarries a coil immersed in a mag- In other words, if it is not desired to record accurately the voice currents or pothe machine gives a faithful reproreally another way of saying that the art must tive of the'excess pressure wave either by Any deriva inte ration'or differentiation is'theoretically- Y obtamable and also intermediate stages.

Although I have describeda paratus using throughout the principle of t e plain mass or non-resonant system cases may arise where the very great sensitivenessinherent in the combination of a microphone and sound concentrhtaing trumpet presents great possibilities. tus can emade to yield most useful results and in combination with a plain mass reencorded asdescribedsuch results can be graved accurately on the wax. v

Similarly it may happen that it is desirable to use the detecting part of the inventilcl n in conjunction with any recording telep one. I

In the accompanying drawings, which illustrate. the invention v Figure 1 illustrates the invention applied to recording on-a disk; 1 I I Figure 21s a plan of the engraving instrument shown in igure 1.

Figure'3 is an enlarged detail view of the recording coil shown in Figure 1.

- Figure 4' instrument applied to recording on a cylinder, an v Figure .5 is va modified form of recording instrument. v a, ,Figure 1 is a diagram "illustrating the principle ical engraving system possessin as near as may be one tone. A detector, w ich may be of the kind described .in my prior specification No. 705,713 (British No. 160223) with sensitive element controls the valve 42, in the plate circuit ofwhich is placed an inductance '43, with iron core 53, and secondary winding 54, which transfers the potential varia tionswith or without alteration of scale as cirs cumstances allow to the valve 44, in the plate circuit of which is placed an inductance 45, a resistance 55 and a condenser 56, all in series, and in parallel 'withthe potential transformer 57 contro 46, which valve operates the coil 1 of the electromagnetic engraving instrument through the transformer 59. The engraving or recording instrument. comprises a coil 1 capabl e of torsional vibration, that is,'elastically plvoted on an axis 5 by means of the wire '69 of which the coil is wound, or if this is either toothick or toothin, by a separate w1re;- Acu'tting stylus; 3 is attached to the of the invention as appliedto a mechan- 1' rimary of a. lling the valve care and experiment such apparais a' view of the same recordingv i cOiL. The wire 69is knotted or otherwise enself represent anything very defimte, wh1ch1 s larged at" 79, so that the screwed ebonite 1w brushes 7l, situated the ebonite lever 65,

pivoted at66, can be used to tension the wire :69, and cause it to.

press tightly against the rubber ads 72, cemented to the lever 65. ,A counterb 73. Figure2 is a plan from above showing the engraving instrument in position between K thepoles 9, 10, of an electromagnet. Wires from the ends '70 of the coil lead to the mercury pools 7 4 and 75 into which the distorted currents are led by the conductors 76 and 7 7 .Figure 3 is a greatly enlarged. transverse sectional view] of the .recordingcoil 1 for recording on-the disk blank 28. It consists preferably'of .two coils 80 and ,81 for pro-.

viding the additional damping mentioned in an'earlier part of the present specification.

These-coils are not'ih electrical connection and one of"them, is the main coil whichreceives the distorted currents The other coil may be more or lessl'shortcircuited. The coils are situated in the magnetic air gap between the other binding from tones likely recording and. constrained by two wires coil is approximately 300 grams on each side.

Figure 4' shows this same engraving device applied-to a cylinder. y t J igure 5 is another form-of'engraving device in which an instrument of the Bell re-' ceiver class is adapted to the case. The valve 46 operates the coil 58 of the electromagnetic engraving instrument through the transformer 59 and the leads 76 .graving instrument 'comprises a permanent and 77. The en magnet 60 of the horse show type with laminated poles 61 and laminated armature 62 "shaped so as to-be as free as possible to interfere with the 63, separated by the width of the armature and by the rubber pad 64, to which one end is cemented. Themagnet is carried by the ebonite bracket'65 pivoted at 66'to a feed-screw.

- carriage not shown and counter-balanced to the poles to be varied. It is to be understood largely determined by these wires.

'to have a frequency of the order of secure the pm the stylus. 3, s An adjustment 68, permits the er gravitational pressure on own engraving the disk 28. block 67, elastically hinged at distance of'th'e armature from that the'wires 63 are stretched by the magnetic force andthat the natural period is For'the system to be practicable itis necessary for it onethouf sand cycles asecond though the best pitch is I a' matter for experiment and varies according to the proportions adopted. .Atthis natural d alancing adjustment is provided at would be about 15,000 c.

fretluency'the electrical system, 45, 55 and 56,.

only allows the transformer 57 to supply the damping losses.

conceivably if the armature were a diaphragm with N tones in an important accoustic region N systems inN valve transformers corresponding to 45, 55 and 56, or possibly in parallel could be incorporated in the scheme.

Again if, as is preferred, in place'of the magnot an armatureand engraving device as in the previous.figures of this specification be used the effect of undue resonance .of the reproducing machine could be -checked in like" I manner. I What I claim is 2- 1. In means for recording sound, anelectromagnetic recorder operating a stylus, which recorder has only a single period of vibration relative toits supporting structure, and valve circuits containinginductanoe, resistance and capacity, for modifying the effect of the natural period of the recording device. 1

tromagnetic recorder operating a stylus,

2. In means for recording sound, an elec which recorder has only a single period of vibration relative to its supporting structure,

and valve circuits forfmodifying the effect of the natural period of the recording device, such valve circuits containing inductance, resistance and capacity, the relation of the inductance and capacity being such that if forming a closed circuit such circuit would have substantially the same frequency-as that of the recording device.

tromagnetic recorder which recorder has only a single period of vibration relative to its supporting structure, and valve circuits for modifying theefl'ect of the natural period of the recording device,

,3. In. means for recording sound, an elec- 4 operating a stylus,-

such valve circuitscontaining inductance,

resistance and capacity in series with the plate circuits, the total impedance of the saidmodifying circuits being small compared with that of the plate circuits.

4. In means for recording sound, an electromagnetic recorder operating a stylus,

which recorder has only a single period of vibration relative to its supporting structure, and an electric correcting means fonmodifying the effect of the natural period of the recording device,

means for the conductor.

such recording devicecomprising the stylus, a conductor and damping 5. In means for recordingsound, an elec- I ,tromagnetic recorder operating a stylus, which recorder has one period of vibration relatlvejto 1ts supporting structure, and an device, such recording device comprising a stylus, a conductor and electromagnetic ampmg means for the conductor.

electric correcting means for modifying the, effect of the natural period of the recording" 6. In means for recording sound, an electromagnetic recorder operating a stylus, which recorder has one period of vibration relative to its supporting structure, and an 5 electric correcting means for modifying the effect of the natural period of the recording device, such recording device comprising a stylus, a conductor and an electromagnetic damping means for the conductor, which 10 damping means consists of a coil carried by the conductor and admitting of any degree of shortcircuiting.

7. In means for recording sound, an electromagnetic recorder operating a stylus,

5 which recorder has only'a single period of vibration relative to its supporting structure, and an electric correcting means for modifying the effect of the natural period of the recording device, which correcting means 20 shall include a device for integrating the lower tones electrically. 1

8. In means for recording sound, an electromagnetic recorder operating a stylus, said recorder having only a single period of 2 vibration relative to its supporting structure,

and valve circuits including impedance elements therein arranged to modify the .efiect of the natural period of the recording device.

In testimony that I claim the foregoing as my inventionI have signed my name this first day of May, 1925.

ADRIAN FRANCIS SYKES. 

